Mercury switch



J. M. JACKSON MERCURY SWITCH Sept. 10, 1940.

Filed Aug. 23, 1938 (Io/11v M (JACKS N,

Patented Sept. 10, 1940 UNITED STATES PATENT OFFICE 4 Claims.

This invention relates generaily to automatic control means and particularly to control means for stopping the operation of a pump actuating mechanism in the event the movement of the me- 5 chanism and connected pump parts becomes accelerated or irregular.

This invention is particularly designed for use in combination with the ordinary type of oil well pumping mechanism and the invention will be 10 illustrated and described in this connection. However, the invention might be used on other types of machinery.

Pumping mechanisms, particularly oil well pumping mechanisms, are usually operated un- 15 attended for long periods of time. The continual stress of raising oil, often from great depths, renders the mechanism subject to unpredictable breakage. When breakage occurs, as often happens, the pump mechanism sufiers considerable damage due to the fact that the motive power continues operating and moving the broken parts, often at increased speed. The motion of the pump mechanism either accelerates or becomes irregular or eccentric as a result of the continued 25 application of power after a breakage of a part.

It sometimes happens that the pumping mechanism will stick appreciably without breaking in which event the movement of the entire mechanism is intermittently slowed down. Since most 30 oil well pumping mechanisms employ a belt drive between the motor and the rest of the mechanism, when the pump sticks it causes the belt to slip thereby creating a fire hazard, the friction of the slipping belt over-heating the belt and its 35 driving and driven pulleys.

Therefore, it is a primary object of the invention to provide an improved control device embodying a mercury switch which may be mount ed on the polish rod of a well pump or some por- 40 tion of the associated Well pumping mechanism which is effective to stop the operation of the motive power when the action of the part on which the device is mounted becomes accelerated, irregular or otherwise eccentric, due to the failure 45 of a part of the pump or pump actuating mechanism.

It is also an object of this invention to provide a device of the character indicated which is en- 50 tirely automatic in its operation and which may be easily and quickly reset for operation after it has been actuated.

It is a further object of" this invention to provide a control device of the type indicated which 55 includes a hermetically sealed switch which is designed to accomplish the closing of an electrical circuit without the formation or passage of sparks or open arcs and thereby eliminate any fire hazard in connection with the operation of the switch.

It is also an object of this invention to provide a device of the character indicated which can be connected in circuit with any suitable motor stopping means so that when the switch of the device is closed, and motor stopping means will function to stop the motor or motive power irrespective of the type of motive power employed. Other mercury switches have been devised which are designed for the same purpose as the switch disclosed herein, but such switches often fail to function quickly if a break occurs in the mechanism during the down stroke of the polish rod of the pump. This is usually due to the fact that a relatively dead pool of mercury is provided which is only more firmly driven in or contained in its reservoir when the switch travels downwardly and is suddenly stopped or has its direction of travel changed.

It therefore is a particular object of this invention to provide a device of the character indicated which includes a mercury switch which is adapted to function when a break occurs in the pumping mechanism on the down stroke of the polish rod and which will function if the switch is traveling downwardly and suddenly stopped or has its direction of travel reversed. To accomplish this object, it is a particular object of this invention to provide a relatively live pool of mercury in the switch which is susceptible to movement out of its normal reservoir means when the switch undergoes the movements just referred to.

It is also an object of this invention to provide a device which is operable from several installation points on the pump operating mechanism 40 and which may be quickly installed and requires no adjustments.

These and other objects will be apparent from the drawing and the following description there of. Referring to the drawing which is for illustrative purposes only:

Fig. 1 is a diagrammatic elevation of a pump actuating mechanism showing the device of this invention in relation thereto;

Fig. 2 is a fragmentary end view of a portion of Fig. 1 showing the device of this invention installed in place;

Fig. 3 is a sectional elevation of the device of this invention;

Fig. 4 is a view similar to Fig. 3 but showing the hinged section of the device in the inverted position; and

Fig. 5 is an end elevation of the mercury switch taken in the direction of line 55 of Fig. 3.

More particularly describing the invention referring to Fig. 1, reference numeral H generally indicates an oil well pumping mechanism including a prime mover l2 which has been shown in the form of an internal combustion engine, a belt is connecting the engine to a reduction gear unit M which drives a counterbalanced crank !6. The crank operates a walking beam i! through the medium of a pitman 18. The beam is supported by a Sampson post i 8 and carries the horsehead 20. The horsehead is connected to a polish rod 2i operating in an oil well 22 by means of the wire line 23. A polish rod clamp 2d secures the wire line 23 to the polish rod 2 i.

The device of this invention generally indicated by reference numeral 25 is designed to be mounted on the upper end of the polish rod above the clamp as shown in Figs. 1 and 2. However the device will work if mounted at other points including the walking beam and pitman. Conductors 26 and 2? lead from the device 25 to the magneto 28 of the motor and ground re spectively. The conductor 2? may be connected to the ground post of the magneto so that when the switch is closed the magneto is grounded or short-circuited, thereby stopping the motor. The device could of course be connected to other motor stopping means and the circuit might also include an audible or visible warning signal of some sort.

Referring to Figs. 3 to 5 for details in the construction of the device of this invention, reference numeral 32 indicates a container or box which may be fabricated from sheet metal provided with a corrosive proof coating or may be constructed of some othermaterial. The box 32 is provided with the flexible clamps 33 by means of which the box may be clamped to the polish rod as indicated or to some other member.

The front of the box is provided with a door or hinged section 3 5 which is hinged at its lower end at 35 and which is adapted to swing outwardly and downwardly to the position in which it is shown in Fig. 4. For convenience the door is provided with a handle 3%. Inside the top of the box 32 is provided a spring catch 3? in which a lug 33 on the door is adapted to engage for the purpose of yieldably holding the door in a closed position.

Mounted on the inner side of this door by means of brackets 45 which may take any suitable form, is a cylindrical holder ii preferably formed of an insulating material which is adapted to house a mercury switch generally indicated by reference numeral 42. The switch is embedded in tar $43 which serves to protect it. It is not essential that holder i! be cylindrical nor that tar be used for embedding the switch.

Referring to the switch 52, this switch comprises a sealed receptacle of insulating material li i having a downwardly extending leg portion 35 forming an electrode well it in the bottom of which are mounted two electrodes i? and 8. The electrodes extend through the container and are electrically connected to the conductors 2t and 2?. Although the conductors 26 and 21 have been shown separated in the diagrammatic representation of Fig. 1, these conductors are preferably housed in a cable E9 which extends through the upper end of the box 32 and is held in place therein by the rubber bushing 50.

The receptacle it also has a second leg portion, indicated by reference numeral 52, which forms a reservoir 53. A connecting portion, or straw tube, 5Q is provided which connects the lower end of the reservoir with the upper end of the electrode well. The straw tube M has less cross sectional area internally than the reservoir for a reason which will subsequently be described. Mercury 55 is provided in the switch and is normally contained in the reservoir 53 and the straw tube 54 as indicated in Fig. 3.

I Preferably the receptacle Mi is formed of glass and is evacuated and subsequently filled with argon gas, however it is not essential to the invention that the switch be so constructed.

With the construction just described there is provided a switch which has a live pool of mercury by reason of the fact that the mercury is normally contained in a reservoir which connects at its lower end with a straw tube in which the mercury is free to rise, the straw tube being of less cross sectional area than the reservoir. Since the quantity of mercury in the reservoir 53 exceeds the quantity in the straw tube 5 when the switch is vertically reciprocated the mercury level in the connecting portion M or straw tube, rises and falls to a greater extent than in the reservoir 53. With this construction, when a break occurs in the pumping mechanism on the down stroke of the polish rod, the switch being mounted thereon, the mercury in the switch, when the downward motion of the switch is suddenly arrested, de-

scends in the reservoir 53 and ascends in the straw tube 54 and spills over from this tube into the well 455 contacting electrodes 47 and '18 thereby completing a circuit through the electrical apparatus previously described.

It should also be apparent that with the construction described mercury may be thrown from the reservoir and connecting straw tube into the electrode well by accelerated motion or eccentric motion of the pumping mechanism caused by failure of some part when the polish rod is traveling upward, however, the regular motion of the mechanism is insufficient to dislodge the mercury from its normal position in the reservoir and straw tube.

After the mercury has been displaced or partially displaced from the reservoir and straw tube into the well i6 and it is desired to reset the switch to break the contact between the terminals All and 68, the door 34 of the box is opened to the position in which it is shown in Fig. 4 and the mercury falls to the upper end of the tube. The door is then gradually returned to its closed position of Fig. 3 and the mercury will flow first into the reservoir 53 and then rise in the straw tube 5 The switch is then reset and again ready for operation.

It should be apparent from the above description that a mercury switch is provided which is adapted to function to close the circuit and stop the prime mover of a well pumping mechanism when a break occurs in some part of the pumping mechanism, the switch being designed to be mounted on some portion of the well pumping mechanism and to be actuated by an irregularity in the movement of the mechanism.

Although the switch has been shown and described with reference to a particular construction, it is within the scope of this invention to change the construction somewhat and it is intended to cover such changes as come within the spirit of the claims.

I claim as my invention:

1. A switch comprising a sealed receptacle of insulating material having two downwardly extending hollow leg portions forming a reservoir and an electrode well respectively; electrodes in the bottom of said electrode well; said receptacle having a hollow connecting portion connecting said reservoir near the bottom thereof with the upper portions of said electrode well; and a highly conductive liquid body in said receptacle adapted to be normally positioned in said reservoir and said connecting portion.

2. A switch comprising a sealed receptacle of insulating material having two downwardly extending hollow leg portions forming a reservoir and an electrode well respectively; electrodes in the bottom of said electrode well; said receptacle having a hollow connecting portion connecting the lower end of said reservoir with the upper portion of said electrode well, said connecting portion being of less internal cross-sectional area than said reservoir; and a highly conductive liquid body in said receptacle normally positioned in said reservoir and said connecting portion.

3. For use as described a switch device comprising a container; a supporting member pivotally mounted on said container and adapted to be swung downwardly to an inverted position; a mercury switch mounted on said supporting member, said switch comprising a sealed receptacle of insulating material having two downwardly extending hollow leg portions forming a reservoir and an electrode well respectively, electrodes in the bottom of said well, said receptacle having a hollow connecting portion connecting the lower end of said reservoir with the upper portion of said electrode well, and mercury in said receptacle; said switch being adapted to be set by downward swinging movement of said supporting member whereby the mercury therein moves from the electrode well into the reservoir and connecting portion and remains therein out of contact with the electrodes on the return movement of said supporting member to its original position.

4. A switch comprising a sealed receptacle of insulating material having an electrode well and a reservoir portion, electrodes in the bottom of said well, said receptacle having a conduit portion connecting the lower end of said reservoir portion with the upper portion of said well, said conduit portion having less capacity than said reservoir portion, and a highly conductive liquid body in said receptacle adapted to be normally positioned in said reservoir and said conduit portion.

JOHN M. JACKSON. 

